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PWM sub zero ? (Read 5,379 times)

Robski Guru Member Picogroup Offline Posts: 262 Yorkshire Great Britain Gender:	PWM sub zero ? Jul 28^th, 2013 at 12:36am I have noticed this now on several captures of PWM control circuits, the PWM drops below zero, why would this be does anyone know ?
Back to top	« Last Edit: Jul 28^th, 2013 at 3:15am by Robski » Seat_Altea_circuit_design_switch_on_640x385.jpg (47 KB \| 506 ) Cheers Rob. IP Logged

brandonb

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Re: PWM sub zero ?
Reply #1 - Jul 28^th, 2013 at 5:07am

its the flyback circuit in action, if it wasn't there you would see huge kick backs like injector wavforms
they use a diode reverse biased across the device or simular design, when the driver cuts off juice, the diode is forced to conduct cycling the electromagetic energy that is now being turned to current back through the device in a small loop until it dissipates, hence negative voltage

i make my living on oem engineering blunders

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Robski Guru Member Picogroup Offline Posts: 262 Yorkshire Great Britain Gender:	Re: PWM sub zero ? Reply #2 - Jul 28^th, 2013 at 5:26am Thanks Brandon, that makes perfect sense
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Darren Cotton Junior Member Offline Posts: 91 United Kingdom England Gender:	Re: PWM sub zero ? Reply #3 - Jul 28^th, 2013 at 11:26am Good question... I have seen this before, but never really thought about why it does this... Good question Robski and thanks Brandon, I think I get it... Darren
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Anthony Lamb Super Nerd Picogroup Offline Posts: 1,202 Brisbane Queensland Australia Gender:	Re: PWM sub zero ? Reply #4 - Jul 29^th, 2013 at 12:45am If i am understanding it correctly it is like a diode in the coil side of a relay? Pretty cool
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